Infrared absorption spectra determination

Shake for 1 minute, allow the layers to separate, and filter the chloroform extracts through separate filters of about 2 g of anhydrous granular sodium sulfate supported on pledgets of glass wool. Extract each aqueous layer with two additional 10 mL portions of chloroform, filtering and combining with the respective main extracts. Evaporate the chloroform solutions under reduced pressure to dryness, and dissolve each residue in 10 mL of carbon disulfide. The infrared absorption spectrum, determined in a 1-mm cell, of the solution obtained from the test specimen exhibits maxima only at the same wavelengths as that of the solution obtained from the Reference Standard (RS). 

A kinetic trace for a particular metal carbonyl intermediate is recorded at a specific wavelength obtained from the time-resolved infrared absorption spectrum. Suitable data analysis allows determination of the kinetics of the decay of the intermediate. 

Identification The infrared absorption spectrum of a 1 50 solution in chloroform, determined in a 0.1-mm cell, exhibits relative maxima at the same wavelengths as those of USP Ethyl Maltol Reference Standard, similarly prepared. 

Epoxy-P-ionone had been reported previously by Viani et al.,(13), Schreler et al., (J 4) and V/obben et al., ( ). In the present study besides the mass spectrum an infrared absorption spectrum was also obtained and was found to be identical to that of an authentic sample. An odor threshold was determined in water solution to be 100 ppb. It is, therefore, a relatively weak odorant and as its concentration, in all fresh tomato samples examined, is well below this figure it seems unlikely that it can contribute to fresh tomato aroma. 

The infrared absorption spectrum of the trimeric chloride has been determined by Daasch and others (24, 25, 46), and is shown, for the sodium chloride region, in Fig. 3. It is dominated by the absorption band at 1218 cm i, which is due principally to the P-N stretching mode and occurs at slightly different positions in the spectra of the other polymers. 

The infrared absorption spectrum of sulfacetamide sodium has been determined in KBr disc (4). The principal peaks appear at 825, 1090,1145,1264,1552,1600 cm 1. The infrared stretching frequencies of the amino group have been used to calculate the force constant, the band angle and the "S" character of the nitrogen orbitals of the N-H band (23,24). Infrared measurements of sulfonamides have been performed to study the imide-amide tautomerism (25) and to see if there is any change in the electronegativity of the SO2 group (26,27). Sulfacetamide in eye-drops and ointments has been identified by attenuated total reflectance (ATR) infrared spectra (28). 

Figure 5 shows the infrared absorption spectrum of the non-modified polybutadiene. The peak at 740 cm is based on the cis-1.4 structure of polybutadiene, and those at 910 cm and at 960 cm are based on the vinyl structure and the trans-1,4 structure, respectively. From these results, the microstructure of the polybutadiene was determined as follows the cis-1.4 content was 97.4X and the trans-1,4 and vinyl contents were 1.2X and 1.4X, respectively. 

In addition to these problems in applying the single-band method to quantitative infrared spectroscopic analysis, the single-band method is not suitable for determining the molar ratios of two or more substances existing in a sample. The single-band method, which depends only on the selected key band, does not utilize all the other bands in the observed infrared spectrum. Thus, it is reasonable to seek an alternative method that makes the optimum use of an entire infrared absorption spectrum for quantitative analysis. 

A majority of traditional NIR measurements are made on solid materials and these involve reflectance measurements, notably via diffuse reflectance. Likewise, in the mid-IR not all spectral measurements involve the transmission of radiation. Such measurements include internal reflectance (also known as attenuated total reflectance, ATR), external reflectance (front surface, mirror -style or specular reflectance), bulk diffuse reflectance (less common in the mid-IR compared to NIR), and photoacoustic determinations. Photoacoustic detection has been applied to trace-level gas measurements and commercial instruments are available based on this mode of detection. It is important to note that the photoacoustic spectrum is a direct measurement of infrared absorption. While most infrared spectra are either directly or indirectly correlated... 

Figure 20-29 Fourier transform infrared spectrum of polystyrene film. The Fourier transform of the background interferogram gives a spectrum determined by the source intensity, beamsplitter efficiency, detector response, and absorption by traces of H20 and C02 in the atmosphere. The sample compartment is purged with dry N2 to reduce the levels of H20 and C02. The transform of the sample interferogram is a measure of all the instrumental factors, plus absorption by the sample. The transmission spectrum is obtained by dividing the sample transform by the background transform.

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